Heat flowable fluororesins having properties such as chemical resistance, nonstickiness, heat resistance, low coefficient of friction, and electrical insulation properties, are also capable of generating pinhole-free coated films and, thus, are useful as coating materials. Heat flowable fluororesins which are used in such coating applications include, for example, copolymers (PFA) of tetrafluoroethylene and perfluoro(alkyl vinyl ether), copolymers (FEP) of tetrafluoroethylene and hexafluoropropylene, copolymers (ETFE) of tetrafluoroethylene and ethylene, and the like. These resins, which are insoluble in water and organic liquids, defy use as solution-type coatings. For example, these resins are applied by an electrostatic application of a powder coating material or used as water-based liquid dispersions stabilized with surfactants and liquid dispersions based on organic liquids where the liquid dispersions are applied to substrates by means, such as spraying, immersing, casting, followed by heating and fusing to generate coated films.
The film coating obtained from electrostatic coating is normally about 50-100 .mu.m thick, while the liquid dispersion coating material gives normally a 20 .mu.m thick film coating. However, this level of thickness is not a sufficient thickness for anticorrosion applications, which leads to the demand for developing a coating material capable of generating a thicker coated film.
In order to solve the above problems, the applicant of this invention previously proposed (Japanese Patent Application Publication 57-15607) a fluororesin liquid dispersion for a thick film coating application comprising a heat flowable fluororesin powder having an average particle size of 2-300 .mu.m and a porosity of not more than 0.74 in a liquid dispersing medium having a surface tension of not more than 45 dyne/cm. This proposal now permits generating a thick 500 .mu.m film if the coated surface is level, but vertical surfaces, or the like, have created problems in that the fluororesin powder would fall off from the coated surface.
For applications requiring corrosion resistance, such as at chemical plants, where the performance is approximately dependent upon the thickness of the film, coating compositions and methods of coating which can form thick films even on vertical surfaces have been desired.